The
coherer was used as a detector about 100 years ago. Coherer is
a device that detects electromagnetic wave. It consists of a
very small quantity of nickel fillings lying looselybetween a couple of metal electrodes. The
electric resistance of a couple of electrodes isusually
high (The coherer is almost insulated state.) however once it
receives the shockelectromagnetic
wave generated from the aerial spark discharge, the coherer
responds sensitively, and the electric resistance decreases
rapidly. (The coherer becomes almost conduction state.)

The
coherer was used as a detector about 100 years ago. Coherer is
a device that detects electromagnetic wave. It consists of a
very small quantity of nickel fillings lying looselybetween a couple of metal electrodes. The
electric resistance of a couple of electrodes isusually
high (The coherer is almost insulated state.) however once it
receives the shockelectromagnetic
wave generated from the aerial spark discharge, the coherer
responds sensitively, and the electric resistance decreases
rapidly. (The coherer becomes almost conduction state.)

After
Herts (Ger.) discovered the electromagnetic wave through
experiment in 1888. Branly (Fr.) found that the electric
resistance decreases when some pieces of metal powder received
theelectromagnetic
wave in 1890. He supposed that the reason is because the metal
powder"coherer"Branly has named the coherer "Radio
Conductor" It is the origin of "coherer"It is said that "radio" means the
electric wave in the beginning. Lodge (U.K) presented thatthe coherer is a wave detector in 1894. In
those days there were not a convenient detectorexcept
the coherers, so they had been produced as detectors for
practical use , and usedin many
countries.

The
coherer has some fatal faults as a device which detects
electromagnetic wave of communication.

〇
The sensitivity
varies every time.

〇
The characteristic
will change in a short term There
are a lot of secular changes.

〇
It is necessary to
give the vibration to the coherer in order to return it to its former

state, so we can not raise the transmission rate.

〇The malfunction by the lightning
is awful. (We can not decode Morse. )

〇It is not possible to use it for
a wireless telephone.

Fleming
(U.K.) a had a hard time in the
improvement of the coherer, and he invented the diodevacuum tube as the fundamental solution in
1904.Picard(U.S.)invented the crystal detector in 1906.It is said that the coherer completed his
roles as a practical detector just dozens of years afterit launched.

In
comparison with breakthrough of the crystal detector or the
diode vacuum tube, cohererhas
not be researched or made improvements as a practical device,
so it has been appearedin one
corner of school textbooks.The
coherer is unusable as a device for the communications now,
but Hirakawa Institute ofTechnology
paid attention to an excellent character as the device for
detecting the lightning.

〇
There is sensitivity to static
electricity. It can detect the lightning
before it strikes.

〇
It has high
sensitivity of the shock electromagnetic wave (impulse
voltage)

such as the lightning. It has low sensitivity
of the broadcast communication wave.

〇

The device
itself is highly selective for the lightning.It can detect the lightning even

under strong electromagnetic field.

〇

The
turning on operation is extremely fast and the turning on
current is
extremely

large.

〇
Impulse withstand
voltage is high. It is hard to break down when close lightning strikes.

The device itself works a surge absorber.

We solved a fault of old coherer and wanted to make a thunder detector with the high durability. And we put a study on an experiment about coherer more than six years.
When the result was never given and was beginning to give up it, we succeeded in producing good
Schottky barrier diode of the comparatively stable sensitivity in materials of old coherer and suddenly developed the situation.
And we completed one movement model about coherer, and the result of the experiment supported it.

As for the coherer, the electrode and metal powder are exposed to air at the time of production.
On an electrode of the coherer and the surface of the metal powder, a thin oxidation film and hydration film are made naturally by the oxygen and water of this air.
This thin oxidation film and hydration film are semiconductors, and the movement of the coherer is caused by the destruction of this semiconductor film.

Even if the thickness of the film was heterogeneous, and it put an electrode and metal powder during a vacuum because it just used a semiconductor film formed naturally in the air in the old coherer, it was the unstable thing which occurred of the big individual difference.

A figure is an electric equivalent figure of the coherer.

When we increase the voltage above a certain level between electrodes of the coherer, it becomes equal that a diode and resistance were connected to series like a figure by an electric field.

An electrode of the coherer and metal powder or contact between the metal powder are point contact. The semiconductor film of the part which a point came in contact with causes a breakdown phenomenon by the voltage and an electric current is concentrated here and drifts.
The semiconductor film of the part which a point came in contact with is destroyed at last by an increasing electric current, and the metal which there is under a semiconductor film becomes a joining state, and, in the electrode interval, it is it with a conductive state.
The movement of so called coherer is fixed after a breakdown phenomenon was caused not the voltage how much electric current flows through the point contact part.

In other words the main electric characteristic of the coherer flows between breakdown voltage
(=Vb) and electrodes, and it is defined in electric flow quantity to do namely electric energy
(=∫W dt) between electrodes by a conductive state.

The lower figure showed an example of the reaction of the coherer for the impulse.
The movement of the coherer is divided into three so that a figure shows it.

The
upper photograph possess a certain new coherer which we
developed in a resistor to limit an electric current, 1.2/50(μsec)
40(kV peak) It is a voltage reply characteristic when it added
an examination surge wave pattern.

The
lower photograph is in condition not to install a resistor to
confine an electric current to the same coherer, and it is a
voltage reply characteristic when it added the same
examination surge wave pattern.
The voltage that coherer works lowers than the upper thing
and, with the voltage that this coherer causes a breakdown
phenomenon, agrees almost.

Hirakawa
Institute of Technology pursed the principle of
operation of coherer by a mordern
semiconductor theory, and we successfully have made it
to revive as a practical electronic device in our time
by using new materials instead of nickel and aluminum.